To learn how to make a porch swing, look at a reputable source, such as This Old House, that has step-by-step directions. Start by using a porch swing kit and applying polyvinyl acetate glue to the end of the tenons and inside the mortises.
Slide the tenon into the mortise to begin assembling the swing. Drive stainless steel screws into the available holes and all the way through the tenon. Assemble the back by gluing and inserting the ends of the seat-back into the mortises of the top rail, and then glue the ends of the slats to the mortises in the rails at the bottom.
Take the side pieces, minus the arms, and glue and screw them together. Attach each of the side pieces to the tenons on the back rails, and to help put them in all of the way, consider using a bar clamp. Now that the frame of the swing is ready, begin assembling the seat. Start with the center seat report and apron before gluing and screwing in the slats. The arm rests are also ready to install, so do that before adding the finishing touches.
Before hanging the swing, insert the bolts into the side pieces, and apply thread-locking glue. Tighten all of the bolts, and leave the rope holes facing up. Fill each screw hole with a plug with glue, apply the finish, and allow everything to dry before hanging.